Increased expression of RUNX2 associated with decreased HDAC4 in OA cartilage. (A-a) X-ray film showed no radiographic changes in the normal controls, whereas there was joint space narrowing and cartilage damage in the OA patients. (A-b) The tibial plateaus from normal control and OA patients were shown (A-c). Safranin O staining was performed to show degeneration in the cartilage from OA patients and the lack thereof in normal control. (B-a, B-b) Immunofluorescent histochemistry was used to show HDAC4 staining (blue: nucleus; red: HDAC4). HDAC4-positive cells (red) were significantly less in OA cartilage than the normal control. The upper boxed region indicates the magnified area shown at the boxed region below. HDAC4-positive cells were decreased to 17% of total cells in OA cartilage compared with 90% in normal control. (C-a) Immunohistochemistry was performed to show expression of Runx2 in OA cartilage and normal control. The boxed region indicates the magnified area shown at the right side. (C-b) The mRNA levels of Runx2 in OA cartilages (n = 3) and normal controls (n = 6) were tested by real-time PCR. (*P <0.05) (C-c,C-d) Western blotting showed expression of Runx2 increased in OA samples compared with the normal control. Semi-quality by densitometry showed the mean concentration of Runx2 in the cartilage of OA patient (n = 3) compared with the cartilage of normal controls (40- to 60-year- olds) (n = 3) (*P <0.05). HDAC4, histone deacetylase 4; OA, osteoarthritis; Runx2, runt-related transcription factor-2.